1. Field of the Invention
This invention relates to an amorphous magnetic alloy with high magnetic flux density intended for use mainly as the magnetic core material for power transformers but also suitable for use as the magnetic core material of saturable reactors, high-frequency transformers, smoothing chokes and other equipment requiring high saturation magnetic flux density and low loss.
2. Description of the Prior Art
As iron base amorphous alloys produced by the liquid quenching method are characterized by extremely low core loss, they have been seen as promising magnetic core materials for power transformers and high-frequency transformers. Nonetheless, they have as yet failed to achieve full-scale practical utilization. The reason for this lies in the fact that their saturation magnetic flux density is considerably lower than that of silicon steel sheet and the fact that they require expensive B as an indispensable alloying element.
The amorphous alloys that have so far been developed and practically applied in power transformers are Fe--Si--B alloys comprising about 78 atomic % Fe and 10 atomic % B. In these alloys top priority is not on saturation magnetic flux density but on amorphous phase formability and thermal stability. They therefore have the disadvantage of somewhat low saturation magnetic flux density (Bs&lt;1.6T at room temperature). As use of a material with a low saturation magnetic flux density makes it necessary to set a low maximum operating magnetic flux density, the core becomes large in volume and weight.
An Fe-Si-B alloy is known to achieve a peak room-temperature saturation magnetic flux of about 1.68T when the Fe content is 82-83 atomic %. One conceivable approach to increasing the saturation magnetic flux density is therefore by increasing the alloy Fe content. This is not practical, however, because in the case of producing wide or thick materials which cool slowly it is difficult to achieve stable formation of ribbon composed solely of amorphous phase and including no crystalline phase. Owing to this, formation of crystalline phase is readily caused by even slight variations in the casting conditions, with the result that the product is degraded or becomes nonuniform in such soft magnetic properties as core loss and permeability. Simply stated, it has not been possible to realize a major improvement in the saturation magnetic flux density of Fe--Si--B alloys without degrading their soft magnetic properties.
Amorphous alloys have higher electrical resistance than conventional soft magnetic metals and are therefore easy to fabricate as thin materials. This means that the advantage of using an amorphous alloy increases with increasing frequency of the application. A notable example of this can be seen in Co base amorphous alloys which exhibit close to zero magnetostriction and also have a small coercive force Hc, properties that have led to practical application in magnetic amplifiers and common mode chokes.
All presently known zero-magnetostriction Co base amorphous alloys have been realized by including various auxiliary elements in the basic CoFeSiB alloy first announced by Kikuchi et al. Typical of these are the alloys disclosed in JP-A-58-31053 and JP-B-63-28483. JP-A-58-31053 relates to the improvement of thermal stability by addition of Ti, V, Cr, Mn, Ni, Zr, Nb, Mo, Ru, Hf, Ta, W and Re to the CoFeSiB alloy, and JP-B-63-28483 to a method for manufacturing a core with a high squareness ratio by annealing a toroidal core of amorphous CoXSiB alloy ribbon in a magnetic field parallel to the periphery thereof, X standing for one or more of Ti, V, Cr, Mn, Ni, Zr, Nb, Mo, Ru, Hf, Ta, W, Re, Fe, Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy.
There are also various other requirements regarding practical constituents. Such other requisites include, for example, that the immunity to influence from lot-to-lot component variation be high, that the range of annealing conditions be broad, that degradation during the core fabrication process be low, and that the anti-corrosion property be excellent. When all of these additional factors are taken into consideration, it becomes clear that the alloys that have been proposed up to now leave much to be desired.